This mug undergoes numerous steps to achieve this bark like look.  It’s created with fine polar ice porcelain. First it is thrown on the wheel, then coated with a chemical, torched, to create an exterior crust then throwing continues and it is stretched from the inside out, breaking the exterior crust. Thus creating the wood look! Hand pressed sprigged shells and barnacles are added, then the rest of the firing and glazing process is done, completing the final look....and yes it is microwave and dishwasher safe! Aprox 10 oz size. 
*Actual mug may vary from photo.